The invention relates generally to a rotor and hammer assembly for use with a size reducing machine. More specifically, the invention relates to a rotor and hammer assembly comprising a drive shaft with a rotor casing sealed by two end plates, and with a plurality of hammer secured to the rotor casing.
Impact crushers, like rotary hammermills or tub grinders, and the like, of the type contemplated herein, are widely used to size reduce objects into smaller fragments through rotation of a motor driven rotor. These devices typically include a plurality of hammers attached to the rotor. During operation the rotor spins allowing the hammers to impact, and thereby size reduce material.
Rotor assemblies used in conjunction with size reducing machine (such as tub grinders, rotary hammermills, vertical feed machines, and the like) experience a number of problems associated with the operation and maintenance of the size reducing machines. For example, the powerful and violent interaction between the rotor assembly and the matter being size reduced causes a great deal of wear on any exposed surfaces, and the interaction between the material in side the machine and the rotor and hammer assembly is difficult to control in a manner that allows for smooth and efficient operation of the machine.
Further, prior art rotor assemblies utilize a complex arrangement of parts. The parts include a plurality of hammers secured in rows substantially parallel to a drive shaft. The hammers secure to a plurality of plates, wherein each plate orients about the drive shaft. The plates also contain a number of distally located throughbores. Pins, or rods, align through the throughbores in the plates and in the hammers. Additionally, spacers align between the plates. All these parts require careful and precise alignment relative to each other. In the case of disassembly for the purposes of repair and replacement of worn or damaged parts, the wear and tear causes considerable difficulty in realigning and reassembling of the rotor parts. Moreover, the parts of the rotor assembly are usually keyed to each other, or at least to the drive shaft, this further complicates the assembly and disassembly process. For example, the replacement of a single hammer can require disassembly of the entire rotor. Given the frequency at which wear parts require replacement, replacement and repairs constitute an extremely difficult and time-consuming task that considerably reduces the operating time of the size reducing machine. In some cases removing a single damaged hammer can take in excess of five hours, due to both the rotor design and to the realignment difficulties related to the problems caused by impact of debris with the non-impact surfaces of the rotor assembly.
Prior art rotor assemblies expose a great deal of the surface area of the rotor parts to debris. The plates, the spacers, and hammers all receive considerable contact with the debris. This not only creates excessive wear, but contributes to realignment difficulties by bending and damaging the various parts caused by residual impact. Thus, after a period of operation prior art rotor assemblies become even more difficult to disassemble and reassemble. Moreover, the effects of this normal wear and tear also contributes to balancing problems, especially considering that the rotor spins at 1100 to 1900 rpm. The design of the prior art rotor assemblies also contributes to the difficulty in balancing the rotor, since the rotor assemblies require balancing from the center shaft out to the hammers. The shock load of the rotor impacts on the hammers, spacers, plates, pins, and the drive shaft. Damage to any part can effect the rotor balance.
Prior art rotor assemblies sometimes attempt to alleviate the problems of alignment by using over-sized components, or in other words deliberately introducing play into the system. The play allows extra room to move the pins in and out, for example. This, however, merely increases the opportunity for debris to wedge between the parts, which further damages the parts, and increases the need for maintenance. In some cases, due to the play in the rotor system, debris can jam the rotor to the point of preventing operation of the size reducing machine. At this point, maintenance and repair becomes extremely difficult, time consuming, and costly.
Another drawback of prior art rotors comprises residual debris impact during operation. Ideally the most efficient operation occurs when only the impact surfaces of the hammer tips encounter the debris. An open rotor assembly exposes the surface of the rotor assembly parts to debris. This not only increases the wear on these parts, but all this residual contact consumes power. Any power directed away from the hammer tips contributes to inefficient operation. The non-wear surfaces of the rotor assembly components simply do not size reduce matter with the efficiency of the hammer tips.
Conventional prior art rotor assemblies arrange the hammers in rows parallel with the axis of the center shaft (or axis of rotation). This means an entire row of hammers strike the debris simultaneously, and this takes a great deal of power. Additionally, this configuration maximizes the amount of strike force transferred to the rotor assembly, which in turn further increases the amount of wear and tear on the system. In practical terms the use of the pins, or rods, to secure the plates and hammers forces the hammers into a configuration that is parallel to the pins. Thus, prior art rotors, generally, can only configure the hammers in straight rows that align parallel to the drive shaft. Accordingly, the prior art rotor assemblies do not easily allow for varying the configuration of the hammers.
Also, prior art assemblies often experience a funneling effect that tends to channel the debris away from the drive end of the rotor assembly. This effect also contributes to inefficient operation through uneven wear across the rotor. This also increases the power required to run the assembly, since part of the assembly in doing more work than the rest of the assembly.
Based on the foregoing, those of ordinary skill in the art will realize that a need exists for a rotor assembly that provides for reduced maintenance, for more efficient operation, and for more flexible repair, replacement, and configuration of the hammers.